In traditional cheesemaking, cheese is prepared by adding a starter culture and rennet to warm milk to form a curd (setting). When the desired consistency and strength of the curd has been obtained, the curd is cut, followed by separation of whey from the curd, e.g. by draining after which the curd is salted, pressed and stored (ripened).
In this process, a considerable loss of milk proteins and--to some extent--fat takes place due to the removal of whey so that the yield of cheese is decreased relative to the total content of proteins and fat in milk. A cheesemaking process has therefore been developed whereby the milk is concentrated, primarily by ultrafiltration, to approximately the fat and protein content desired in the finished product after which a starter culture, rennet and salt are added. No significant whey drainage occurs from the curd, and therefore the whey proteins (notably .beta.-lactoglobulin and O-lactalbumin) normally lost when the whey is removed are retained in the concentrate resulting (together with retained fat) in an increase in yield of about 10%.
However, the use of UF-concentrated milk for making cheese has only been commercially successful for a limited number of cheese types. A major cause of this is the effect of whey proteins on the characteristics of the resulting UF cheese. Thus, it has been found that undenaturated whey proteins are resistant to hydrolysis by rennet, starter culture proteases and plasmin (De Boer and Nooy, North European Dairy Journal 46, 1980, pp. 52-61; De Koning et al., Netherlands Milk and Dairy Journal 35, 1981, pp. 35-46; Quist et al., Beretning fra Statens Mejeriforsog, 1986, p. 268). The undenaturated whey proteins may act as a filler resulting in cheese with a smoother texture. The change in texture is thought to be ascribable to the fact that the whey proteins do not participate in the formation of the casein matrix which is essential for the strength and firmness of many cheeses, in particular cheeses with a low moisture content, or may even negatively affect the matrix if present in an amount of up to 20% of the protein dry matter. It has further been observed that the whey proteins may negatively influence the process of cheese ripening in that they may have a dilution effect by lowering the proportion of casein in the curd (De Koning et al., supra) or that they may limit the accessibility of casein to the enzymes responsible for ripening.
The problem of decreases maturation rate of UF cheese cannot be overcome by denaturing the whey proteins, e.g. by heat treatment of the cheese milk, as it has been found that the presence of denatured whey proteins in certain UF cheeses adversely affect their stretch and melt properties on heating (Covacevich and Kosikowski, Journal of Dairy Science 61, 1978, pp. 704-709; Quist et al., supra; Olson, Dairy Record 85(7), 1984, p. 85). Furthermore, hydrolysis of denatured whey proteins may give rise to atypical flavours and textures of the ripened cheese (Green et al., Journal of Dairy Research 48, 1981, pp. 333-341; Brown and Ernstrom, Journal of Dairy Science 65, 1982, pp. 2391-2395; Banks and Muir, Journal of the Society of Dairy Technology 38, 1985, pp. 27-32). Denatured whey proteins may also affect the maturation rate in a similar fashion as undenaturated whey proteins, as discussed above.